Elimination of fading by diversity factor



June 21, 1932. H. O. PETERSON 1,863,695

ELIMINATION OF FADING BY DIVERSITY FACTOR Filed June 19, 1925 4 Sheets-Sheet l flvwamtoz HAROLD o. PETERSON June 21, 1932. 0 PETERSON 1,863,695

ELIMINATION OF FADING BY DIVERSITY FACTOR Filed June 19, 1925 4 Sheets-$heet 2 In? W flwmw/g Jaw June 21, 1932. H O PETERSON 1,863,695

ELIMINATION OF FADING BY DIVERSITY FACTOR Filed June 19, 1925 4 Sheets-Sheet 3 aflvmioz HAROLD O. PETERSON agy hia June 21, 1932. H. o. PETERSON ELIMINATION OF FADING BY DIVERSITY FACTOR Filed June 19, 1925 Fly. 4

4 Sheets-Sheet 4 /j mum Patented June 21, 1932 UNITED STATES HAROLD O. PETERSON, 0F RIVEBHEAD,'NEW YORK, ASSIGNOR TO RADIO CORPORATION Parser crates f 0J5 AlVIER-ICA, A CORPORATION OF DELAWARE ELIMINATION OF FADING BY DIVERSITY FACTOR Application filed June 19,

This arrangement relates to the use of an apparatus designed to tend to preventand reduce the effects of the phenomenon co1nmonly known as fading of wireless signals when received by a single receiver, and also to eliminate to more or less extent the interference caused by static andother stray dis turbances. I

It is well known that when a receiving set is sharply tuned'to a single wave length, and is receiving signals from a transmitter which is also sharply tuned to the same wave length a considerable distance away, difliculty is often had with the signals dying down and becoming inaudible at various intervals. In some localities this is a very gen eral phenomenon while in. others it occurs less frequently. lhe arrangement of this. invention is intended to overcome this difficulty and can be used with long wave lengths or with short ones, though probably its most important use will be found with the shorter wave lengths, because with these the trouble is especially prevalent and most annoying.

Long wave lengths have been most commonly used for long distance communication up until very recently. However, it has been found that short wave lengths used for sending and receiving by wireless have advantages not found with the longer ones. For instance, there is less static disturbance, less absorption and the directional effects produced in directional antennae systems is much sharper and better defined. With the former arrangements, however, reliable operation on short waves has been verydifiicult over long distances and often times practically impossible, because of fading, even though over short distances short waves can be used with success. 7

Various theories regarding-the phenomenon of fading have been advanced. Perhaps one of the better known and apparent ly logical ones is that based on the Heaviside layer theory This theory assumes that above the surface of the earth there is a layer ofstratified and partially conducting air or atmosphere of some sort which has a reflective eilect upon wireless waves impinging on 1925. Serial m. 38,165.

it. Since it is true that there are some waves which travel on the surface of the earth and others which extend upwardly, that path taken by the upwardly extending waves, after having been reflected by the Heaviside layer, will be greater in length than that taken by the waves travelling on or near the surface. Therefore there is a possibility that the upwardly extending waves will be some distance behind in phase, relative to'those that extend along the surface, when they meet. V

I F or this reason the waves meeting at the receiving point may be 180, degrees out of phase, and if they are equal in magnitude, no signalwill be had, for the two waves will cancel each other. It will be readily seen that this will not occur at all points along the surface of the earth where receiving stations may be located, hence, if reception can be had from several places at the same time and the results of the reception brought to a central point, the efiect of fading at any one receiver will be reduced. This invention deals with arrangements for producing these results. 7

Prior arrangements for obtaining directional signalling and for reducing the eifect of static haveused a plurality of antennae and have attempted to combine the various signal energies directly and in phase or to heterodyne them to produce beats and then I isa variable.

An explanation of this is suggested by the Heaviside layer theory, for although a strata of conducting atmosphere lies considerable distance above the surface of the earth, this layer is by no means stationary.

Particularly at daybreak and sunset when the suns rays are increasing or diminishing, is this effect most noticeable. It is suggested that this is due to the ionizing effect of the suns rays. At nigl1t,the Heaviside layer rises to a height considerably above that in It has been found that fading in the longer wave lengths varies slowly, while the shorter I ones vary very rapidly and in a disturbing way probably caused by the unstationary surface of the layer and undulations in it. This accounts for the greater diflicultiesexperienced with shorter waves.

This'invention also has for its purpose the use of several antennae for averaging up and producing a signalwhich will vary only in proportion to the number of antennae used, but the resulting signals are combined independently of the phase of "the received high frequency signal energy. 1 Variation caused by the action described willpr oduce an averaging result on the several antennae. If a large number of points are taken, separated a number of wave lengths apart on a direct.

line from the sending station, the chance of fading at all of these places at the same time is small.

When high frequencies are sent over ordi-' nary transmission lines for any appreciable distance the effect of attenuation .must be taken into consideration. Thus, if-.a wave of varying intensity and high frequency be sent considerable difficulty will be had in keeping the various intensities separated. In this invention the frequency is reduced by means of modulation to a point at which it can more easily be transmitted.

As was already remarked, it has been found that-the waves impinging upon two antennae separated any appreciable distance apart are not always in phase with each other nor does the phase relation between the two remain the same at differenttimes. When two antennae are so located, at times the wave will vary in phase in a very undesirable way. For instance, when the wave length of 100 meters is used and the two antennae are separated several miles apart, a complete phase reversal between the two stations has sometimes been found to take efiect every few .2. Generationof a second high frequency.

at the receiver, modulating it: with audio fre- I quency energy generated a central station,

stitute arrangement.

to the audio frequency period. With this 7 method the undesirable effects of attenuation, high frequency phase difi'erences, etc., are avoided because the sending of the signal over the transmission lines at a low frequency isnot affected by these. Also detection and amplification may be had at each antenna and transmission and combination of'the resulting audio frequencies had as beforeg v V It has been found that so far as a practical application of this invention goes that when a frequency is used in the neighborhood of 100 meters for-'sending-and'a separation of antennae a distance of 500 feet or less than two wave lengths, an appreciable improvement may be had. If more antennae are used andvarious other distances of separationare used, a proportionally greaterimpro'vement will be found. Thus, within a small area considerably better reception is used with shortwave lengths.

possible when I v lVherever local or territorial fading is in advance known to exist use may be made of thisknowledge. Thus in some places where localized fading is present, small separation of antennae would be suflicient. Other places .where very generaly fading is the rule, separation at greater distances would be necessary. .However, where generalfading is present and greater separation of the antennee is required this greater separation would take care of difiiculty encountered in case the fading should become more or less localized.

This idea ofdiflerent'fading and different phase relations is called the principle ofdiversity factor of the various places and relations in question.

To accomplish theseresults the following arrangements are disclosed and reference is made to Figs. 1 to l inclusive of the annexed drawings.

Fig.1 shows a general method of carrying out my invention.

Fig. 2 shows a substitute arrangement for one of the receiving stations.

Fig. 3 shows a modification of this sub- Fig. 4 shows an arrangement whereby the sametransmission line may be used for both,

receiving and transmitting the modulating frequency.

1, 2, 3,-etc., represent a series of geographically spaced antennae and may or may not be separated by distances greater than one Wave length apart. These antennae systems are coupled to the modulators 4, and 6 which are controlled by the couplings 7 10, 8, 11 and 9, 12 through a transmission line 13. The output from a source of audio frequency, or of a radio frequency which is modulated at an audio rate, is sent over this transmission line as indicated at 22.

Thus, the result of the signal received on the antennae and the modulating Wave is had in the couplings 14, 15 etc. These oscillations are detected as at 16, 17, etc. and appear in the output circuits 18, 19, 20, etc. The audio frequency will not appear when no signal is received because the modulators 4, 5, etc. are balanced. The output circuits are all coupled to the return transmission line 21' to which is connected the receivers or equivalent signal translating arrangement 23.

\Vhenever a signal is received on the antennee, the oscillations produced are modulated by an audio frequency or both a radio frequency and an audio frequency. With this with other similar methods heretofore used.

For all practical purposes the audio frequency phase variations caused by radio fre-.

quency phase variations of the received signals is so slight as to be negligible.

Various other arrangements can be used for modulating the oscillations as received on the antennae.

Fig. 2 shows one of these other methods. 24 may be oneof the receiving antennae to which is coupled an intermediate frequency modulator 25, the modulating coil being shown at 26.

From any suitable local or central source high frequency oscillations are introduced at 27, causing an intermediate frequency .wave

- plings 32, 33 at an audio rate. The intermediate frequency components of the audio modulated frequency appears in the output coupling 34 and is led to a detector 35 which may be connected to the transmission line from 36. In this case the high frequency modulation is separated from the audio frequency modulation so that a greater range of control may be efiectedon'the receiving system.

The different modulating arrangements can be either located at the respective receivers or may be at the central receiving sta impressed upon this oscillator through the couplings 41,, 42 so that the oscillations affecting the modulator tube are, in turn, modulated at an audio rate.

. The output of the modulator 38 is'transmitl ted through the coupling 43 into the intermediate frequency amplii'ier 44 Which, with its output'coil 45, may be coupled to a detector 46. This detector produces the audible signals in the connections 47 which may be transmitted over a transmission line tothe central receiving station or used in any other advantageousarrangement. I

Thus, when a signal is received on the an.- tenna 37, it is impressed on the modulator circuit 38 and results in an intermediate frequency output. If We assume that the audio frequency is represented by 7%, that the frequency produced in the high frequency oscillator is f and the frequency of the re ceived signal is f then we have in the output coil 43 of the modulator 38, the frequencies f f and fr f f All these frequencies appear in the detector 46, butthe output of this detector gives only 7, which is the orignal audio frequency introduced at 42.

In the case of the arrangement in Fig. 2 if the signal frequency is f the high frequency impressed, f then there appears in theoutput circuit of the modulator 25 the frequency f -f Assuming that f, which is induced at33 is an audio frequency tone then the modulator 31 will have in its output coil 34the same frequencies as Werefound in the case of Fig. 3 and the detection is carried out by detector 35 in a like manner producing the audio .frequency output 7% at 36.

If it is desirable to use only one transmission line, an arrangement can be used as in Fig. 4 where 1, 2' etc. are the antennae and 4' 5, etc., are the intermediate frequency. modulator and amplifier. These intermediate frequency modulators are supplied by modulated heterodyne frequency at the tions thereby permitting individual control coupling 7,, 10 and 8, 11 over the connections 48 and 49 through the condensers 55, '56 and 57, which permit only the high frequencies generated at 59 to pass through. Choke coils 52 and 53 are arranged to prevent these frequencies from afiecting the other parts of the'system. Thus, proper modulated frequencies 'arefound at-l4, 15 and are detected at 16, 17' giving the. desired low audio frequencies at 18 19?, which are coupled to the transmission line at 54. These separately received signals are-combined in ing stations are used considerable of the effect of static and other disturbances is eliminated. This is true because usually such disturbances are of more or lesslocal nature and the ratio of the total signal received at the.

central receiving station is by fargreater when a local disturbance. affects only one of the several antennae than. it wouldbe if only one antenna were used and the total effect of the disturbance were felt on this antenna. In this way the greater the/number of antennae and the more diversely located they are, the greater the advantage of this system will be. This is true both in respect to static and similar disturbances and to fad ing.

It is obvious that either of the arrangements or modifications shown in Figs. 2 and 3 might well be used in connection with the single transmission line arrangement shown in Fig- 4L without departing from the spirit of this invention. Other minor and obvious modifications and substitutions may also be made. T e locations of the various oscillating sys tems. and modulating circuits need not be limited as shown but may well be arranged at any desired place. 4,

With these arrangements, the troublesome effects from attenuation over long distance transmission lines whenhigh frequency is used are obviated. It can be seen from this arrangement that receptionat various points different distances from each other is had, and is centralized at a common point to pro.-

. duce a better result. For fading occurring at any one of these stations at different times an average result is produced which causes the relative intensity at the receiver to be practically constant. This can be accomplished only when aconsiderable number of antennae are used and distributed according to the known conditions of that particular 10- cality. At some points it might be found necessary to use only two antennm stations, as shown, since it might befound that fading would not be present at the same time at these points. a 2

While I have described my invention in a more or less specificway, it is notintended tolimit it to these particular arrangements. In the claims which follow I shall by the term .signal initiated energy mean energywhich is present only when a signal is received, and I- intend it to include signal energy, amplified signal energy, and heterodyned signal energy.

W'hatI claim is.: a V 1. The method of receiving signal oscillations which includes intercepting the signal oscillationsat various points, generating an audio frequencyoscillation at another point, transmitting the audioffrequency oscillation to the various points, combining the audio frequency .with signal. initiated oscillations,

and detecting and transmitting the result to 3. The method of diversity factor reception for reducing fading. effects at relatively short wave lengths" which includes collecting signal energyat a plurality of. separated points, ateach of said points modulating signal initiated energy with generatedaudio frequency energy, detecting the modulated energies to reproduce audio frequency energies, combining the audio frequency energies, and translating the combined energy.

4. The method of diversity: factor reception for reducing fading effects at relatively short wave lengthswhich includes collecting signal energy at a plurality of separated points, at each of said points modulating signal initiated energy with generated audio frequencyenergy,suppressing the audio frequency componentsof the modulated energies, detecting the higher frequency components of the modulated energies to reproduce audio frequency energies only when signal energy is received,.combining the audio. frequency energies, and translating the combined energy.

-' 5. The method' 'ofdiversity factor reception for reducing'fading effects at relatively short wave lengths which includes collecting signal, energy at aplurality of. separated points, generating audio frequency energy atacentral point, using the audio frequency energy to' modulate signal initiated energy at each of said separated points, detecting the modulated energies to reproduce audio fre-v quency, energies, combining the audio frequency energies, and translating the combined energy. t

6.. Themethod ofqdiversity factor 'recep I tion "for reducing fadingefiects at relatively.

short wave lengths which includes collecting signal energy at a plurality of separated points, generating audio frequency energy at a central point, using the audio frequency to modulate signal initiated energy at each of said points, suppressing the audio frequency components of the modulated energies, detecting-the higher frequency components of the modulated energies to reproduce audio frequency energies only when signalenergy is received, combining the audio frequency energies, and translating the combined energy.

7. The method of diversity factor reception for reducing fading effects at relatively short wave lengths which includes collecting signal energy at a plurality of separated points, combining the signal energies with generated heterodyne energy at each of said points, modulating the combined energies with generated audio frequency energy, detecting the modulated energy to'reproduce audio frequency energies, combining the audio frequency energies, and translating the combined energy.

8. The method of diversity factor reception for reducing fading effects at relatively short wave lengths which includes collecting signal energy at a plurality of separated points, combining the signal energies with generated heterodyne energy at each of said points, modulating thecombined energies with generated audio frequency energy, suppressing the audio frequency components of the modulated energies, detecting the higher frequency components of the modulated energies to reproduce audio frequency energies only when signal energy is received, combining the audio frequency energies, and translating the combined energy.

9. The method of diversity factor reception for reducing fading effects at relatively short wave lengths which includes collecting signal energy at a plurality of separated points, heterodyning the signal energy at each of said points with generated heterodyning energy, generating audio frequency energy at a central point, using the audio'frequency energy to modulate the combined energies at each of said separated points, detecting the modulated energies to reproduce audio frequency energies, combining the audio frequency energies, and translating the combined energy.

10. The method of diversity factor recep tion for reducing fading effects at relatively short wave lengths which includes collecting signal energy at a plurality of separated points, fheterodyning the signal energy at each of said pointswith generatedheterodyning energy, generating audio frequency en ergy at a central point, using the audio frequency energy to modulate the combined energies at each of said separated points, suppressing the audio frequency components of the modulated energies, detecting the higher ing the audio frequency energies, and translating the combined energy.

11. The method of diversity factor reception for reducing fading eflects at relatively short wave lengths which includes collecting signal energy at a plurality of separated points, generating audio frequency energy at a central point, generating high frequency energy at a central point, combining the centrally generatedenergy with the signal energy at each of said separated points, detecting the combined energies to reproduce audio frequency energies, combining the audio fre quency energies, and translating the, combined energy. 7

12. The method of diversity factor reception for reducing fading efiects at relatively short wave lengths which includes collecting signal energy at a plurality of separated points, generating audio frequency energy at a central point, generating high frequency energy at a central point, combining the centrally generated energy with the signal energy at each of said separated points, suppressing the audio frequency components of the combined energies, detecting the higher frequency components of the combined energies to reproduce audio frequency energies only when signal energy is'received, combining the audio frequency energies, and translating the combined energy.

13. The method of diversity factor recep tion for reducing fading effects at relatively short wave lengths which includes collecting signal energy at a plurality of separated points, generating audio frequency energy at a central point, generating high frequency energy at a central point, using the high frequency energy to heterodyne the Signal energies at each of said separated points to produce intermediate frequencyenergy, modulating the intermediate frequency energies with the audio frequency energy, detecting the modulated intermediate frequency energies to reproduce audio frequency energies, combining the audio frequency energies, and translating the combined energy.

14. The method of diversity factor reception for reducing fading effects at relatively short wave lengths which includes collecting signal energy at a plurality of separated points, generating audio frequency energy at a central point, generating high frequency energy at a central point, using the high frequency energy to heterodyne'the signal energies at each of said separated points to produce intermediate frequency energy, modulating the intermediate frequency energies with the audio frequency energy, suppressing the audio frequency components of the modulated energies, detecting the higher frequency components of the modulated energies to reproduce audio frequency energies only when signal energy is received, combining the audio frequency energies, and translating the combined energy.

15. An arrangement for diversity factor reception for reducing fading effects at relatively short wave lengths comprising means for collecting signal energy at a plurality of separated points, means for modulating the signal initiated energies with genera-ted audio frequency energy, means for detecting the modulated energies to reproduce audio frequency energies, means for combining the 7 audio frequency energies, and means to trans late the combined energy.

16. An arrangement for diversity factor reception for reducing fading effects at relatively short wave lengths comprising means for collecting signal energy at a plurality of separated points, balanced modulators for modulating the signal initiated energies with generated audio frequency energy and for suppressing the latter, means for detecting the modulated energies to reproduce audio frequency energies when signal energy is received, means for combining the audio frequency energies, and means to translate the combined energy.

17. An arrangement fordiversity factor reception for reducing fading efiects at relatively short wave lengths comprising means for collecting signal energy at a plurality of separated points, a central source of audio,

frequency energy, means for modulating the signal initiated energies at each of said points with the audio frequency energy, means for detecting the modulated energies to reproduce audio frequency energies, means for combining the audio frequency energies, and means to translate the combined energy.

18. An arrangement for diversity factor reception for reducing fading effects at relatively short wave lengths comprising means for collecting signal energyat a plurality of separated points, a central source of audio frequency energy, a balancedmodulator at each of said points for modulating the signal initiated energies with the audio frequency energy and for suppressing the latter, means for detecting the modulated energies to reproduce audio frequency energies when signalenergy is received, means for combining the audio frequency energies, and means to translate the combined energy. 7

19. An arrangement for diversity factor reception for reducing fading effects at relatively-short wave lengths comprising means for collecting signal energy at a plurality of separated points, means to combine the signal energies with generated heterodyne energy at each of said points, means for modulating the combined energies with generated audio frequency energy, means for detecting the modulated energies to reproduce audio frequency energies, means for energies with generated heterodyne energy, a balanced modulator at each of said points for modulating the combined energies With generated audio frequency energy and for suppressing the latter, means for detecting the modulated energies to reproduce audio frequency energies whensignal energy is received, means for combining the audio frequency energies, and means to translate the combined energy. 1

21. An arrangement for diversity factor reception for reducinglfading'effects at relatively short wave lengths comprising means for collecting signal energy at a plurality of separated points, means to heterodyneithe signal energy at each of said points, a central source of audio frequency energy, means for modulating the combined energies with the audio frequency energy, means for detecting the modulated energies to reproduce audio frequency energies, means for combiningthe audio frequency energies, and'means to trans late the combined energy.

22.An"arrangement for diversity factor reception for reducing fading effects at relatively shortwave lengths comprising means for collecting signal energy at a plurality of separated points, means to heterodyne the signal energy at each of said pointsrwith generated heterodyning energy, a central source of audio frequency energy, a balanced modulator at each of said points for modulating the combined energies with the audio frequency energy and'for suppressing the latter, means for detecting the modulated energies to reproduce audio frequency ener gies when signal energy i's-received, means for combining the audio frequency energies, andmeans to translate the'combined energy. 23. An arrangement for diversity. factor reception for reducing fading eflects at relatively short wave lengths comprising means for collecting signal energy at a plurality of separated points, a central source of audio frequency energy, a central source of high frequency energy, means for combining the centrally supplied energy with the signal energy at each of said points, means for detecting the'combined energies to reproduce audio frequency energiesgmeans for combining the audio frequency energies, and

means to translate the combined energy.

24. An arrangementfor diversity factor reception for reducing fading effects at relatively short wave lengths comprising means for collecting signal'energy at a pluralityof separated points, acentral source of audio frequency energy, a central source of high frequency energy, means to. combine the centrally supplied energy with the signal ener y at each of said points and for suppressing t e audio frequency energy, means for detecting the combined energies to reproduce audio frequency energies when signal energy is received, means for combining the audio frequency energies, and means to translate the combined energy.

25. An arrangement for diversity factor reception for reducing fading effects at relatively short wave lengths comprising means for collecting signal energy at a plurality of separated points, a central source of audio frequency energy, a central source of high frequency energy, means to heterodyne the signal energies with the high frequency energy to produce intermediate frequency energies, means for modulating the intermediate frequency energies with the audio frequency energy, means for detecting the modulated intermediate frequency energies to reproduce audio frequency energies, means for combining the audio frequency energies, and means to translate the combined energy.

26. An arrangement for diversity factor reception for reducing fading effects at relatively short wave lengths comprising means for collecting signal energy at a plurality of separated points, a central source of audio frequency energy, a central source of high frequency energy, means to heterodyne the signal energies with the high frequency energy to produce intermediate frequency energies, abalanced modulator at each of said points for modulating the intermediate frequency energies with the audio frequency energy and for suppressing the latter, means for detecting the modulated energies to re produce audio frequency energies when signal energy is received, means for combining the audio frequency energies, and means to translate the combined energy.

27. The method of diversity reception for reducing fading effects at relatively short wave lengths which includes making a plurality of radio frequency energy collections having relatively different fading characteristics, transforming each of the collected energies into a form which is independent of the phase of the received radio frequency energy, combining the transformed energies, and translating the combined energy.

28. The method of diversity reception for reducing fading eflects at relatively short wave lengths which includes making a plurality of radio frequency energy collections of relatively difierent fading characteristics, locally generating energy, separately utilizing each of the collected energies for controlling thefiow of locally generated energy independently of the phase of the received radio frequency energy, combining the resulting energies, and translating the combined energy.

29. The method of diversity reception for reducing fading effects at relatively short wave lengths which includes making a plurality of radio frequency energy collections of relatively different fading characteristics,

locally generating audio frequency energy, separately utilizing each of the collected energies for controlling the'fiow of the locally generated audio frequency energy independ ently of the phase of the received radio frequency energy, combining the resulting en ergies, and translating the combined energy.

30. A. diversity receiving system'for reducing fading effects at relatively shortwave lengths comprising a plurality of antennae having relatively different fading characteristics, means for separately transforming each of the received energies into a form which is independent of the phase of the received radio frequency energy, means to combine the transformed energies, and means to translate the combined energy. v V

31. A diversity receiving system for reducing fading effects at relatively short wave lengths comprising a plurality of antennae having relatively different fading characteristics, a local source of energy, means responsive to each of the collected energies for separately cont-rolling the flow of the locally generated energy independently of the phase of the received radio frequency energy, means to combine the resulting local energies, and means to translate the combined energy.

32. A diversity receiving system for reducing fading effects at relatively short wave lengths comprising a plurality of antennae having relatively different fading characteristics, a local source of audio frequency energy, means responsive to each of the collected energies for separately controlling the flow of the locally generated energy independently of the phase of the received radio frequency energy, means to combine the resulting local energies, and means to translate the combined energy.

33. The method of diversity reception for reducing fading effects at relatively shortwave lengths which includes making a plurality of radio frequency energy collections having relatively different fading characteristics, transforming each of the collected energies into ener ies which may be additively combined independently of the phase of the received radio frequency energy, combining the transformed energies, and translating the combined energy. I

34. The method of diversity reception for reducing fading effects at relatively short Wave lengths which includes making a plurality of radio frequency energy collections having'relatively different fading characteristics, locally generating alternating electrical energy,transforming each of the collected energies, with the aid of the locally generated energy, into energies which may be additively combined independently ofthe phase of the received radio frequency energy,com-

bining the transformed energies, and translating the combined energy,

35. A diversity receiving system for reducing fadin efiects at relatively short Wave lengths comprising a plurality of antennae having relatively different fading characteristics, means for collecting radio frequency energy, means for transforming each of the collected energies into energies which may be additively combined independently of the phase of the collected radio frequency energy, means to combine the transformed energies, and means to translate the combined energy.

36. A diversity receiving system for reducing fading effects at relatively short wave lengths comprising a plurality of antennae having relatively different fading character- 7 istics, means for collecting radio frequency energy, a local source of energy, means for transforming each of the'collected energies, with the aid of the locally generated energy, into energies which may be additively combined independently of the phase of the radio frequency energy collected, means to combine the transformed energies, and means to translate the combined energy.

HAROLD O. PETERSON, 

